1. Field of the Invention
The present invention relates to a light emitting apparatus which utilizes an organic electroluminescence cell as a surface emitting light-source.
2. Description of the Related Art
An organic electroluminescence cell has high luminous efficiency as being driven by direct current of low voltage and is capable of being lightened and thinned. Recently, a product which utilizes organic electroluminescence cells arranging to be dot matrix-shaped, for example, as a display has been provided. Further, not limited to the abovementioned display, the organic electroluminescence cell has been receiving attention in being utilized as a light-source of surface emitting.
A number of patent applications have been filed in utilizing the abovementioned organic electroluminescence cells as light-source of surface emitting. Japanese Patent Application Laid-open No. 2006-228557 and Japanese Patent Application Laid-open No. 2006-228457 are examples of such applications.
It is known that electrons injected from a negative electrode side and positive holes injected from a positive electrode side are recombined in a light emitting functional layer which is sandwiched by both of the electrodes when direct current voltage is applied between the opposing electrodes and that the energy thereof performs light emission as exciting fluorescent material. Accordingly, in order to introduce the light from the light emitting functional layer to the outside, a light permeable electrode (that is, a transparent electrode) is used for at least one of the electrodes.
For example, oxide such as ITO (indium tin oxide) and IZO (indium zinc oxide) is used for the abovementioned transparent electrode. In general, the transparent electrode of the abovementioned ITO and the like is coated on a transparent substrate. Then, the light emitting functional layer which includes organic material is formed on the transparent electrode and the opposing electrode which is made of metallic material, for example, is formed on the light emitting functional layer. Thus, the light from the light emitting functional layer is introduced to the outside of the cell after penetrating the transparent electrode and the substrate.
Here, electric resistivity of the oxide such as ITO and IZO constituting the transparent electrode is approximately 1×10−4 Ωcm which is one or two digits higher than electric resistivity of metallic material. Therefore, in a case that a surface emitting light-source of which area is large is formed, large voltage drop occurs at the transparent electrode and unevenness occurs in light emission luminance.
The light emission luminance of the organic electroluminescence cell is to be proportional to current amount injected per unit area of the cell. Therefore, in a case that the transparent electrode is an exhaustive electrode of which area is relatively large, there arises a problem that the luminance becomes low by being affected by the voltage drop at the transparent electrode as being apart from a power supply point against the transparent electrode.
Then, patent applications have been filed for suppressing occurrence of the luminance unevenness by providing auxiliary electrodes of which resistance value is low in order to decrease the voltage drop at the transparent electrode. For example, it has been disclosed in Japanese Patent Application Laid-open No. 2004-134282, Japanese Patent Application Laid-open No. 5-226076 and Japanese Patent Application Laid-open No. 2002-156633.
A configuration of arranging a metallic auxiliary electrode which is formed as a long-shape along the outside of the long side of the transparent electrode is disclosed in Japanese Patent Application Laid-open No. 2004-134282. Further, a configuration of arranging a frame-shaped auxiliary electrode which is made of metallic material, for example, along the periphery of the transparent electrode is disclosed in Japanese Patent Application Laid-open No. 5-226076. Furthermore, a configuration of superposing an auxiliary electrode which is formed as a lattice-shape over the whole transparent electrode is disclosed in Japanese Patent Application Laid-open No. 2002-156633.
However, in the configurations disclosed in Japanese Patent Application Laid-open Nos. 2004-134282, 5-226076, and 2002-156633, there is a problem that luminance difference occurs within a plane between a position where the auxiliary electrode is arranged and a position where the auxiliary electrode is not arranged and even luminance cannot be obtained within the plane. For example, when the auxiliary electrode is formed as a stripe-shape, there arises a problem that a stripe-shaped light variation occurs along the position of auxiliary electrode arrangement.
In order to solve this problem, a surface emitting apparatus (a lighting apparatus) is disclosed in Japanese Patent Application Laid-open No. 2006-19251. In this application, an opening portion is formed by intermittently removing a light emitting functional layer which includes organic material and an opposing electrode portion thereon, and then, positive voltage is applied to a transparent electrode in a spot-like manner via a salient-shaped conductor portion which is connected to the third electrode.
With the configuration of Japanese Patent Application Laid-open No. 2006-19251, it is described that the problem indicated in Japanese Patent Application Laid-open No. 2004-134282 can be solved since positive voltage of the same electric potential is applied to the transparent electrode in a spot-like manner via the third electrode and the salient-shaped conductor portion. However, there remains a problem that the periphery of the position at which the positive voltage is applied in a spot-like manner emits light brightly and the position which is apart from the positive voltage applying point emits light darkly.
Further, with the configuration of Japanese Patent Application Laid-open No. 2006-19251, the light emitting functional layer which includes organic material does not exist at the position at which the salient-shaped conductor portion is located, namely, the position at which the positive voltage is applied in a spot-like manner. Therefore, there is not light emission at this position. Accordingly, there is a problem that the unevenness of the light emission becomes striking due to the non-light-emitting position.